Staged combustion with piston engine and turbine engine supercharger

ABSTRACT

A combustion engine method and system provides increased fuel efficiency and reduces polluting exhaust emissions by burning fuel in a two-stage combustion system. Fuel is combusted in a piston engine in a first stage producing piston engine exhaust gases. Fuel contained in the piston engine exhaust gases is combusted in a second stage turbine engine. Turbine engine exhaust gases are used to supercharge the piston engine.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/412,420 filed Sep. 20, 2002 and titled “Staged Combustion with PistonEngine and Turbine Engine Supercharger.” U.S. Provisional ApplicationNo. 60/412,420 filed Sep. 20, 2002 and titled “Staged Combustion withPiston Engine and Turbine Engine Supercharger” is incorporated herein bythis reference.

The United States Government has rights in this invention pursuant toContract No. W-7405-ENG-48 between the United States Department ofEnergy and the University of California for the operation of LawrenceLivermore National Laboratory.

BACKGROUND

1. Field of Endeavor

The present invention relates to staged combustion and more particularlyto staged combustion with piston engine and turbine engine supercharger.

2. State of Technology

International Patent Application No. WO 92/06285 to Russell A. Stanley,published Apr. 16, 1992 provides the following state of technologyinformation, “As reliance upon the internal combustion engine grows inour modern society, several driving factors have led to the demand forchanges in the design and operation of such engines. As the availablefuel supply slowly decreases, it is an objective of internal combustionengine design to provide for improved fuel consumption and economy whilenot adversely impacting the desired performance of such engines.Alternatively, increasing demands to satisfy environmental concernsassociated with such engines have led to the need for providing complexsystems to reduce emissions of noxious gases such as unburnedhydrocarbons and nitrous oxides formed in the combustion process ofinternal combustion engines. These objectives in the design of internalcombustion engines create conflicting design problems to a great extentas used to reduce emissions of noxious gases have tended to increasefuel consumption and vice versa.”

International Patent Application No. WO 98/49438 to WestinghouseElectric Corporation, published Nov. 5, 1998, provides the followingstate of technology information, “Numerous approaches for improving thethermal performance of combustion turbine power generation systems havebeen proposed since the early 1950s when combustion turbines were firstapplied for stationary power generation. Alternative approaches rangefrom advanced toping and bottoming cycles, to advanced turbine firingconditions. Some of these approaches have been put into practice toreach the current level of performance that combustion turbine powergeneration has evolved to today.

The prevalent factor enhancing performance has been increases in firingconditions (temperatures and pressures) through advances in airfoildesign, materials and cooling methods. Cycle variations are also beingdeveloped to improve system performance in contrast to hardwareimprovements, such as evaporative cooling cycles, recuperative cycles,intercooled cycles, humid air cycles, reheat cycles, advanced bottomingcycles, and elevated steam bottoming conditions. Many proposedapproaches for advanced combustion turbine power cycles have beenrejected as being unworkable or uneconomical, and some have not yet beendeveloped sufficiently to be verified, demonstrated and commercialized.Therefore, a need exists for new, viable approaches for improved powergeneration.”

U.S. Pat. No. 6,089,855 issued Jul. 18, 2000 to Frederick E. Becker etal and assigned to Thermo Power Corporation, provides the followingstate of technology information, “The market for industrial combustionequipment in the United States is shaped in large part by federalregulations governing air standards in urban areas, as mandated by theClean Air Act (CAA), as amended. Industrial expansion can be limited inareas that do not meet National Ambient Air Quality Standards (NAAQS)for the emissions of certain combustion gases, such as NO.sub.2. Newsources of NOx in non-attainment areas must use emission offsets and atight level of control known as “lowest achievable emission rate(LAER).” A target NOx emission no greater than 9 ppmvd (parts permillion by volume on a dry basis with 3% O.sub.2 in the emission) isusually established for new sources in non-attainment areas. The CleanAir Act also sets standards for ambient ozone in non-attainment areasand in other areas called “ozone transport regions,” which meet thestandard but into which ozone can migrate. New sources in some of theozone non-attainment areas will be subject to the same LAER NOx targetlevels. The 1990 amendments to the CAA affects smaller sources thanprevious regulations and consequently will impact industrial scalefurnaces and boilers directly. The usual method to reduce NOx emissionsto meet the LAER standards is to post-process exhaust gases employingselective catalytic reduction.”

SUMMARY

Features and advantages of the present invention will become apparentfrom the following description. Applicants are providing thisdescription, which includes drawings and examples of specificembodiments, to give a broad representation of the invention. Variouschanges and modifications within the spirit and scope of the inventionwill become apparent to those skilled in the art from this descriptionand by practice of the invention. The scope of the invention is notintended to be limited to the particular forms disclosed and theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

The present invention provides a combustion engine method and system. Inone embodiment the present invention provides a combustion engineapparatus comprising a first stage piston engine, fuel, means forcombusting the fuel in the a first stage piston engine in a first stageproducing piston engine exhaust gases with the piston engine exhaustgases containing the fuel, a second stage turbine engine operativelyconnected to the first stage piston engine, means for combusting thefuel contained in the piston engine exhaust gases in the second stageturbine engine producing turbine engine exhaust gases; and means forsupercharge the first stage piston engine using the turbine engineexhaust gases. Various embodiments of the present invention provide acombustion engine method and system with one or more benefits includingincreased boost pressure, increased mean operating pressure, increasedpower density, increased fuel efficiency and reduced polluting exhaustemissions.

In one embodiment the present invention provides a combustion enginemethod with increased fuel efficiency and reduced polluting exhaustemissions by burning fuel in two stages comprising the steps ofcombusting the fuel in a piston engine in a first stage, the step ofcombusting the fuel in a piston engine in a first stage producing pistonengine exhaust gases, the piston engine exhaust gases containing thefuel, combusting the fuel contained in the piston engine exhaust gasesin a second stage turbine engine, the step of combusting the fuelcontained in the piston engine exhaust gases in a second stage turbineengine producing turbine engine exhaust gases and using the turbineengine exhaust gases to supercharge the piston engine.

The invention is susceptible to modifications and alternative forms.Specific embodiments are shown by way of example. It is to be understoodthat the invention is not limited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated into and constitute apart of the specification, illustrate specific embodiments of theinvention and, together with the general description of the inventiongiven above, and the detailed description of the specific embodiments,serve to explain the principles of the invention.

FIG. 1 illustrates a system for increasing engine efficiency.

FIG. 2 illustrates a free wheeling turbine engine.

FIG. 3 illustrates two-staged combustion where the primary combustion isin piston engine and the secondary combustion is in a turbine engine.

FIG. 4 is a simplified flow diagram illustrating the present invention.

FIG. 5 shows a turbine engine supercharger combined with a reciprocatingSI or CI engine.

FIG. 6 shows a turbine engine supercharged reciprocating engine withSCNEA, bypass valve, turbine engine starter, and fuel injector.

FIG. 7 shows a mixing unit for diesel fuel rich exhaust gas and air/NEA.

FIG. 8 shows a turbine engine supercharged reciprocating engine withmixing unit.

FIG. 9 shows the ignition delay as a function of the fuel-air ratio.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, to the following detailed description,and to incorporated materials, detailed information about the inventionis provided including the description of specific embodiments. Thedetailed description serves to explain the principles of the invention.The invention is susceptible to modifications and alternative forms. Theinvention is not limited to the particular forms disclosed. Theinvention covers all modifications, equivalents, and alternativesfalling within the spirit and scope of the invention as defined by theclaims.

Referring now to FIG. 1, a system for increasing engine efficiency isillustrated. The system provides a turbo supercharged reciprocatingdiesel engine. The turbo supercharged reciprocating diesel engine isdesignated generally by the reference numeral 100. The engine section101 includes a piston 103 in a piston chamber 104 driven by a piston rod105. The exhaust gases 106 from the engine section 101 are provided tothe turbine 102. The turbine 102 includes a turbine blade 107. An airintake 108 is driven by the turbine 102. The air is directed through anintercooler 111 that includes cooling tubes 112 with water 109 directedto the cooling tubes and a water outlet 110.

The exhaust gases from the reciprocating engine section 101 are used todrive a turbine that is used to compress the air before it goes into thecombustion chamber. Turbo-charging increases the operating pressure andmass flow in the engine resulting in higher power for a specific enginevolume. Turbo charging is not usually done in a spark ignition enginebecause engine knock occurs with increased pressure and density.Turbo-charging is frequently done with compression ignition or dieselengines to increase performance. Although turbo-charging can increaseengine performance, it does not reduce pollution in the exhaust gases.During normal or cruising operations combustion engines operate fuellean or with excess air to control polluting exhaust emissions.

Referring now to FIG. 2, a free wheeling turbine engine is illustrated.The free wheeling turbine engine is designated generally by thereference numeral 200. The free wheeling turbine engine 200 includesdiesel and cylinders 201, turbocompressor starter 202, compressor 203,turbine 204, igniter and flame control 205, combustion chamber 206,exhaust manifold 207, fuel pump 208, regulator 209, by-pass 210, andpreheating system 211. The power output of a diesel engine can beincreased using the Hyperbar diesel concept where the conventionalturbo-charger is effectively replaced by a free wheeling turbine engine.The freewheeling turbine engine can add energy to the diesel engineexhaust gases to allow higher boost pressures without excessive pumpinglosses. A bypass valve is used to operate the turbine separately tostart the diesel engine. The diesel and turbine engines operate fuellean to control polluting exhaust emissions.

Referring now to FIG. 3, a combustion engine method and system thatprovides increased fuel efficiency and reduces polluting exhaustemissions by burning fuel in a two stage combustion system isillustrated. The combustion engine method and system is designatedgenerally by the reference numeral 300. The method and system 300provides a turbine engine supercharger and a piston engine to reducepollution while increasing or maintaining overall system performance andefficiency. The piston engine operates fuel rich where most of the heatof combustion is released. The piston engine's exhaust gases havesufficient fuel remaining for a second burn in a turbine enginesupercharger. Part of the energy from the piston engine combustion gasesis used to perform work. The cooled combustion gases from the pistonengine are reheated by the second combustion at or near stoichiometricconditions in the turbine combustion chamber. Energy is extracted usinga turbine to supercharge the piston engine and to compress the air forthe turbine engine. Nitrogen enriched air can be used instead of air tofurther control the combustion temperature and products. The air isenriched with nitrogen using air separation technologies such asdiffusion, permeable membrane, absorption, and cryogenics. The methodand system 300 has uses in the replacement and/or modification ofcurrent piston engines to reduce pollutants while maintaining relativelyhigh combustion and thermal efficiencies.

Increasing fuel efficiency in combustion engines while simultaneouslyreducing polluting exhaust emissions has been researched over the past25 years and subsidized by the Federal Government. Maximum fuelefficiency normally occurs at or near stoichiometric conditions wherethe fuel is completely oxidized. In practice the combustion process inan engine is usually with air and not with pure oxygen. When oxygen issupplied by dry air, 3.76 moles of nitrogen will accompany one mole ofoxygen. The stoichiometric air-fuel ratio is the ratio of the mass ofair to the mass of fuel to result in stochiometric combustion. Theactual operating condition of an engine is usually expressed in terms ofthe equivalence ratio which is the ratio of the stoichiometric air-fuelratio to the actual air-fuel ratio. The equivalence ratio is 1.0 whenthe engine is operating at stoichiometric conditions. When an engineoperates at an equivalence ratio greater than 1.0 it is operating fuelrich and produces pollutants such as hydrocarbons (HC), carbon monoxide(CO) and particulate matter. At equivalence ratios less than 1.0 theengine produces oxides of nitrogen (NOx) which is major source orphotochemical smog and is regulated. Also the combustion gases can bevery corrosive with the excess oxygen and reduce the life of the engine.

Past research developed efficient engines by operating with equivalenceratios less than one, but will not meet impending requirements forgreatly reduced NOx. Current research includes the development ormodification of engines such as Variable Compression, Hyperbar Diesel,Homogenous Charged Compression Ignition HCCI, and nitrogen enriched aircombustion. Emissions can also be reduced using catalytic converters forspark-ignited engines or using the Plasma-Assisted Catalytic Reduction(PACER) process for lean-burn engines.

By increasing the combustion temperature and pressure, the efficiency ofa combustion system can usually be increased. The efficiency of theBrayton cycle generally increases with temperature and pressure, but candecrease with pressure when the temperature is too low. Hence it isimportant to operate at the highest temperature as possible to obtainhigh efficiency. The maximum operational temperature of most combustionsystems, especially continuous flow ones, is limited by the materials ofconstruction and the corrosive and oxidative products of combustion. Ingeneral higher operational temperatures decrease the materials physicalproperties (e g., strength) and increase corrosion and oxidation of thematerial.

Typically gas turbines operate with excess air (phi=0.4–0.7) to reducethe operational temperature but produces large amounts of corrosive andoxidative gases. A two-staged turbine can be used to reduce thecorrosive and oxidative gases by burning fuel rich in the first stageand stoichometrically in the second stage. However, in order to obtainacceptable combustion temperatures in the first stage the fuel ratiotends to be excessively high which can result in soot formation andfouling. Another approach to reduce the combustion temperature is to usenitrogen augmentation or enriched air.

Air separation technologies are used to enrich nitrogen in air up to100%. To obtain reasonably high efficiency the fuel andnitrogen-enriched air are combusted at stoichometric conditions thatrequire relatively large amounts of highly enriched nitrogen oxidant.

Referring again to FIG. 3, the combustion engine system 300 will bedescribed in greater detail. The combustion engine system 300 providesincreased fuel efficiency and reduces polluting exhaust emissions byburning fuel in a two stages. A first stage piston engine 301 isprovided for combusting the fuel in a first stage. The first stagepiston engine 301 can be a compression ignition engine, a homogenouscharged compression ignition engine, a variable compression engine, anitrogen enriched air combustion engine, a rotating engine, a linearengine, and/or a reciprocating engine. The first stage piston engine 301produces piston engine exhaust gases and said piston engine exhaustgases containing said fuel. A second stage turbine engine 302 isprovided for combusting the fuel contained in the piston engine exhaustgases in a second stage. The second stage turbine engine producesturbine engine exhaust gases. A supercharger is provided for superchargethe piston engine using the turbine engine exhaust gases.

The first stage piston engine 301 can be a compression ignition engine,a homogenous charged compression ignition engine, a variable compressionengine, a nitrogen enriched air combustion engine, a rotating engine, alinear engine, and/or a reciprocating engine. The fuel can be oil,methane, natural gas, ammonia, alcohols and/or ethers. The fuel in otherembodiments can be any combustible matter. Examples are, fossil fuelsincluding oil, natural gas, and/or coal; inorganic fuels includingammonia, hydrazine, and/or calcium; and organic fuels includingalcohols, ethers, and/or wood. A compressor provides compressed air tothe second stage turbine engine for combusting the fuel contained insaid piston engine exhaust gases.

The piston engine 301 includes a piston 303 in a piston chamber 304driven by a piston rod 305. The exhaust gases 306 from the piston engineare provided to the turbine engine 302. The turbine engine 302 includesa turbine 307 and an air intake 308. The exhaust gases 306 from theturbine 307 are used to compress the air before it goes into the pistonengine 301. The compressed air is directed through an intercooler 311that includes cooling tubes 312 with water 309 directed to the coolingtubes and a water outlet 310. Turbo-charging increases the operatingpressure and mass flow in the engine resulting in higher power for aspecific engine volume. Turbo charging is not usually done in a sparkignition engine because engine knock occurs with increased pressure anddensity. Turbo-charging is frequently done with compression ignition ordiesel engines to increase performance. Although turbo-charging canincrease engine performance, it does not reduce pollution in the exhaustgases.

The combustion engine method and system 300 provides a combustion methodthat uses two-staged combustion where the primary combustion is inpiston engine (e.g., spark ignition (SI), compression ignition (CI)engine and homogenous charged compression ignition (HCCI)) and thesecondary combustion is in a turbine engine. The primary and secondarycombustion can use air or nitrogen enriched air for the oxidizer in thecombustion process.

Referring now to FIG. 4, a simplified flow diagram illustratescombustion engine method that provides increased fuel efficiency andreduces polluting exhaust emissions by burning fuel in a two-stagecombustion system. The combustion engine method is designated generallyby the reference numeral 400. The combustion engine method 100 comprisesthe steps of combusting the fuel in a piston engine in a first stage401. The step of combusting the fuel in a piston engine in a first stage101 produces piston engine exhaust gases 402. The piston engine exhaustgases 402 contain fuel. The step of combusting the fuel contained in thepiston engine exhaust gases in a second stage turbine engine 402produces turbine engine exhaust gases 404. The turbine engine exhaustgases 404 are used to supercharge 405 the first stage piston engine.

The first stage piston engine can be a compression ignition engine, ahomogenous charged compression ignition engine, a variable compressionengine, a nitrogen enriched air combustion engine, a rotating engine, alinear engine, and/or a reciprocating engine. The fuel can be oil,methane, natural gas, ammonia, alcohols and/or ethers. The fuel in otherembodiments can be any combustible matter. Examples are, fossil fuelsincluding oil, natural gas, and/or coal; inorganic fuels includingammonia, hydrazine, and/or calcium; and organic fuels includingalcohols, ethers, and/or wood. A compressor provides compressed air tothe second stage turbine engine for combusting the fuel contained in thepiston engine exhaust gases.

The piston engine operates fuel rich thereby producing a reducingatmosphere and suppressing the formation of NOx. Most of the fuel isburned in the piston engine but the piston engine exhaust gases aresufficiently fuel rich for a second burn in the turbine engine. Thepiston engine in one embodiment is a compression ignition engine thathas heterogeneous combustion resulting in the fuel in the piston engineexhaust gases being near stoichiometric conditions or slightly fuelrich. The step of combusting the fuel contained in the piston engineexhaust gases in a second stage turbine engine occurs nearstoichiometric or slightly fuel lean conditions at reduced combustiontemperatures where NOx formation rate is low.

The turbine engine exhaust gases supercharge the piston engine.Compressed air is delivered to the turbine engine for the step ofcombusting the fuel contained in the piston engine exhaust gases in asecond stage turbine engine. The residence time of combusting the fuelcontained in the piston engine exhaust gases in the turbine engine isincreased to ensure that all hydrocarbons and particles are burned. Thestep of combusting the fuel contained in the piston engine exhaust gasesin a second stage turbine engine stage is combusted with an oxidizerstream. The oxidizer stream in one embodiment is air. The oxidizerstream in one embodiment is nitrogen-enriched air. The nitrogen-enrichedair in one embodiment is produced using air separation technologies. Theair separation technologies can include cryogenic, absorption, diffusionand/or permeation.

The steps of combusting in the combustion engine method 100 takes placeto perform work. In one embodiment the steps of combusting takes placeto provide heat. The heat can be used for a furnace, for a boiler, for asmelter, and/or for an Otto engine. In one embodiment the piston engineis a compression ignition engine and excess air that is added in theturbine engine is increased to ensure that all hydrocarbons andparticles are burned. In one embodiment the piston engine is a sparkignition engine that is operated fuel rich to suppress engine knock. Inone embodiment the step of combusting the fuel in a piston engine in afirst stage is combusted with an oxidizer stream. The oxidizer streamcan be nitrogen enriched air.

Referring now to FIG. 5, another embodiment of a combustion method andsystem is illustrated with a turbine engine supercharger combined with areciprocating SI or CI engine. This embodiment is designated generallyby the reference numeral 500. The piston engine 501 includes a piston503 in a piston chamber 504 driven by a piston rod 505. The exhaustgases 506 from the piston engine are provided to the turbine engine 502.The turbine engine 502 includes a turbine 515 and an air intake 508. Theexhaust gases 506 from the turbine 515 are used to compress the airbefore it goes into the piston engine 501. Fuel rich exhaust 514 isdirected into combustion chamber 513. The exhaust gases 506 are directedthrough an intercooler 511 that includes cooling tubes 512 with water509 directed to the cooling tubes and a water outlet 510. Turbo-chargingincreases the operating pressure and mass flow in the engine resultingin higher power for a specific engine volume. Turbo charging is notusually done in a spark ignition engine because engine knock occurs withincreased pressure and density. Turbo-charging is frequently done withcompression ignition or diesel engines to increase performance. Althoughturbo-charging can increase engine performance, it does not reducepollution in the exhaust gases.

The primary combustion occurs in the reciprocating engine and is fuelrich, that is, at an equivalence ratio greater that 1.0 to provide areducing atmosphere to reduce or eliminate NOx formation. The primarycombustion exhaust gases will have fuel molecules such as CO and H2 insufficient amounts such that they can be burned in the combustionchamber of the turbine engine. The secondary combustion occurs at ornear stoichiometric conditions at a lower combustion temperature whereNOx is difficult to form. The burned gases from the secondary combustiondrive a turbine that in turn drives a compressor that supercharges thepiston engine and provides compressed air for the secondary combustion.Nitrogen enriched air can be used in the primary or secondary combustionprocess to better control the combustion temperature and products.

Two-stage combustion with a CI engine can be used to significantlyreduce HCs and particles in the a-exhaust with the second burn in theturbine combustion chamber. The residence time in the turbine combustionchamber can be increased and excess air can be added to ensure that allof the HC and particles are burned.

The embodiment 500 results in lower pollutant emissions, lower corrosionrates of combustion and heat-transfer equipment, and compatible orimproved efficiencies as compared to the typical combustion process usedin boilers, burners, turbines, and internal combustion engines. Theembodiment 500 involves burning the fuel in two or more stages, wherethe fuel is combusted fuel-rich with nitrogen-enriched air in the firststage, and the fuel remaining after the first combustion stage iscombusted in the remaining stage(s) with air or nitrogen-enriched air.All the combustion stages except the last have a slightly richfuel/oxidant mixture, and the last stage has the stoichometric (or nearstoichometric) fuel/oxidant mixture. The optimum nitrogen concentrationrange for the nitrogen-enriched air is about 85–89% nitrogen (molarpercent), and is adjusted to achieve the desired combustion temperatureand reduced corrosion and pollutant levels. This method of burning fuelsubstantially reduces the oxidant loading (i.e., O₂ and O) and pollutantloading (i.e., NO and CO) in the effluent gas, and is applicable to manytypes of combustion equipment, including: boilers, burners, turbines,internal combustion engines, and many types of fuel including hydrogenand carbon-based fuels. This method of burning fuel, is termed “StagedCombustion with Nitrogen-Enriched Air” or SCNEA.

SCNEA, involves burning fuel in two or more stages in a combustionsystem, where the fuel is combusted fuel-rich with nitrogen-enriched airin the first stage, and then the fuel remaining after the firstcombustion stage is burned in the remaining stage(s) with air ornitrogen-enriched air. All the combustion stages, except the last have aslightly rich fuel/oxidant mixture, and the last stage has astoichometric (or near stoichometric) fuel/oxidant mixture. Followingeach combustion stage, part of the energy from the combustion gases isused to perform work or to provide heat. The equivalency ratio for thefirst stage of combustion and the nitrogen-enriched air are adjusted toachieve the desired combustion temperature and reduced corrosion andpollutant levels. The equivalency ratio and nitrogen enrichmentconcentration ranges are respectively typically, phi=1.1–1.5 and 83–88%.This method of burning fuel substantially reduces the oxidant (i.e., O₂and O) and pollutant levels (i.e., NO and CO) in the effluent and, thus,allow higher operational temperatures to maintain or increase thethermal efficiency. This combustion method is applicable to many typesof combustion systems, including boilers, burners, turbines, internalcombustion engines, and many types of fuel including hydrogen andcarbon-based fuels.

Application of SCNEA to a two-stage gas turbine combustion system can besummarized. First, air is enriched in nitrogen using air separationtechnology and then compressed in a water-cooled compressor to 30atmospheres. The nitrogen enriched air enters the first stage combustionchamber where it is mixed with fuel and bums fuel rich. The combustiongases exit the combustion chamber and enters a turbine at the combustiontemperature of 1700K and the pressure of 30 atmospheres. Work isperformed in the turbine by expansion of the gases to a temperature of780 k and a pressure of 2 atmospheres. The cooled combustion gases enterthe second stage where nitrogen-enriched air or air is added to burn theremaining fuel in the second stage. The nitrogen-enriched air or air issupplied by a compressor and heated in a heat exchanger by the secondstage exhaust gases.

In a two-stage turbine cycle, the first compressor feed consists ofnitrogen-enriched air mixed with the fuel (methane for our example) at350K and a pressure of one atmosphere. The first compressor compressesthe gas mixture to the desired pressure (this compression increases thegas temperature). The mixture is then combusted at a constant pressure.Nitrogen-enriched air is used as the oxidant stream in the firstcombustion stage to allow precise control of the combustion temperature(and correspondingly the pollutant generation) while producing effluentgases that have a very low oxidant loading. The combustion products athigh temperature and an elevated pressure ace expanded to 2.0atmospheres and work is extracted (this expansion results in a loweringof the gas temperature). Since the first combustion stage is operatedfuel-rich (˜>1), there is enough fuel remaining in the effluent from thefirst combustion stage to be flammable when mixed with a stoichometricamount of air (or nitrogen-enriched air). This mixture is combusted at aconstant pressure, of 2.0 atmospheres in the second combustion stage.The temperature of the second combustion stage is maintained below thetemperature of the first combustion stage by controlling the amount offuel remaining after the first combustion stage. The effluent from thesecond combustion stage is then expanded to 1.0 atmospheres and work itsagain extracted.

The thermodynamic cycle of compression-combustion-expansion is theBrayton cycle. For the ideal Brayton cycle, the compression andexpansion (turbine) stages are assumed to be adiabatic and isentropic,and the combustion stage is assumed to be isobaric. The efficiency ofthe Brayton cycle can be increased sometimes by increasing the maximumpressure. However, if the temperature is too low, an increase inpressure can result in a decrease in efficiency.

If the compression ratio is above 15 the temperature should be at least1400K. The low oxidant loading in the effluent when using the SCNEAmethod allows both higher temperatures and higher pressures withoutincreasing corrosion rates over those of typical combustion facilities.These allowable increases in temperature and pressure, when using theSCNEA method, lead to higher Brayton cycle efficiencies.

First Compression—The nitrogen-enriched air and methane mixture is inputto the compressor at 300K and 1.0 atmosphere. The compressor increasesthe pressure of the gas mixture to 30 atmospheres, and because thecompressor is assumes to be water-cooled, the compressed gas is assumedto exit the compressor at a temperature of 350K.

First Combustion Stage—The methane and nitrogen-enriched air mixture at30 atmospheres and 350K is input to the first combustion chamber wheremost of the methane is burned and the temperature is increased to 1700K.

The relative amount of fuel and air in the combustion mixture isdescribed by φ, the ratio of mass fuel to mass air divided by the ratioof mass fuel to mass air for a stoichometric mixture [i.e., (MassFuel/Mass Air)/(Mass Fuel/Mass Air)₂]. For φ>1 the mixture is fuel-richand for φ<1 the mixture is fuel-lean.

It is important to ensure that the gas mixture anticipated for the firstcombustion stage is flammable. Two-staged combustion with a SI enginecan be used to suppress engine knock by increasing the ignition delay.

Referring now to FIG. 6, another embodiment of a combustion method andsystem is illustrated with a turbine engine supercharger combined with areciprocating SI or CI engine. This embodiment is designated generallyby the reference numeral 600. The piston engine 601 includes a piston603 in a piston chamber 604 driven by a piston rod 605. The exhaustgases 606 from the piston engine are provided to the turbine engine 602.The turbine engine 602 includes a turbine 607 and an air intake 608. Theexhaust gases 606 from the turbine 607 are used to compress the airbefore it goes into the piston engine 601. Fuel rich exhaust 614 isdirected into combustion chamber 613. The compressed air directed isthrough an intercooler 611 that includes cooling tubes 612 with water609 directed to the cooling tubes and a water outlet 610. Referring toFIG, 6 a bypass valve is placed in front of the piston engine. Duringstart up the valve is closed and the piston engine is bypassed. Astarter to the turbine engine is turned on to turn the compressor thatcompresses air that flows to the turbine combustion chamber. The fuelinjector injects fuel into the turbine combustion camber and the igniteris turned on to combust the fuel and air. Once the turbine is operatingto the appropriate level, the piston engine bypass valve is opened tostart the piston engine. Air separation units with air coolers can beused to supply nitrogen-enriched air to either or both the piston andturbine engines. The bypass valve can be adjusted to divert extra air tothe turbine engine where fuel is injected to assist faster acceleration.A fuel injector 615 adds fuel to the fuel rich exhaust. An igniter/flamecontrol unit 616 maintains the ignition in the combustion chamber 613.The exhaust has low NO₂, HCl, CO. An intercooler 619 and air separationunit 618 is connected to the turbine engine 602. A turbine enginestarter 621 is connected to the turbine engine 602.

Referring to FIG. 7, a mixing unit 700 can be added between the pistonengine and turbine engine. The mixing unit 700 is used to promote mixingof the piston engine fuel rich hot exhaust gases with air/NEA. Themixing process makes a well-stirred fuel and oxidizer mixture to improvethe combustion process in the turbine combustion chamber. The mixingunit is designed to increase residence time for the mixing by suitablyarranging the flow paths. The mixing unit can also be designed topromote turbulent mixing and reduce heat losses in the mixing process.

Turbo-charging increases the operating pressure and mass flow in theengine resulting in higher power for a specific engine volume. Turbocharging is not usually done in a spark ignition engine because engineknock occurs with increased pressure and density. Turbo-charging isfrequently done with compression ignition or diesel engines to increaseperformance. Although turbo-charging can increase engine performance, itdoes not reduce pollution in the exhaust gases.

The primary combustion occurs in the reciprocating engine and is fuelrich, that is, at an equivalence ratio greater that 1.0 to provide areducing atmosphere to reduce or eliminate NOx formation. The primarycombustion exhaust gases will have fuel molecules such as HC, CO and H2in sufficient amounts such that they can be burned in the combustionchamber of the turbine engine. The secondary combustion occurs at ornear stoichiometric conditions at a lower combustion temperature whereNOx is difficult to form. The burned gases from the secondary combustiondrive a turbine that in turn drives a compressor that supercharges thepiston engine and provides compressed air for the secondary combustion.Nitrogen enriched air can be used in the primary or secondary combustionprocess to better control the combustion temperature and products.

Two-stage combustion with a CI engine can be used to significantlyreduce HCs and particles in the a-exhaust with the second burn in theturbine combustion chamber. The residence time in the turbine combustionchamber can be increased and excess air can be added to ensure that allof the HC and particles are burned.

Referring now to FIG. 8, another embodiment of a combustion method andsystem is illustrated with a turbine engine supercharger combined with areciprocating SI or CI engine. This embodiment is designated generallyby the reference numeral 800. The piston engine 801 includes a piston803 in a piston chamber 804 driven by a piston rod 805. The exhaustgases 806 from the piston engine are provided to the turbine engine 802.The turbine engine 802 includes a turbine 807 and an air intake 808. Theexhaust gases 806 from the turbine 807 are used to compress the airbefore it goes into the piston engine 801. Fuel rich exhaust 814 isdirected into combustion chamber 813. The compressed air directed isthrough an intercooler 811 that includes cooling tubes 812 with water809 directed to the cooling tubes and a water outlet 810. The mixingunit 700 is shown added between the piston engine 801 and turbine engine802.

The embodiment 800 results in lower pollutant emissions, lower corrosionrates of combustion and heat-transfer equipment, and compatible orimproved efficiencies as compared to the typical combustion process usedin boilers, burners, turbines, and internal combustion engines. Theembodiment 300 involves burning the fuel in two or more stages, wherethe fuel is combusted fuel-rich with nitrogen-enriched air in the firststage, and the fuel remaining after the first combustion stage iscombusted in the remaining stage(s) with air or nitrogen-enriched air.All the combustion stages except the last have a slightly richfuel/oxidant mixture, and the last stage has the stoichometric (or nearstoichometric) fuel/oxidant mixture. The optimum nitrogen concentrationrange for the nitrogen -enriched air is about 85–89% nitrogen (molarpercent), and is adjusted to achieve the desired combustion temperatureand reduced corrosion and pollutant levels. This method of burning fuelsubstantially reduces the oxidant loading (i.e., O₂ and O) and pollutantloading (i.e., NO and CO) in the effluent gas, and is applicable to manytypes of combustion equipment, including: boilers, burners, turbines,internal combustion engines, and many types of fuel including hydrogenand carbon-based fuels. This method of burning fuel, is termed “StagedCombustion with Nitrogen-Enriched Air” or SCNEA.

SCNEA, involves burning fuel in two or more stages in a combustionsystem, where the fuel is combusted fuel-rich with nitrogen-enriched airin the first stage, and then the fuel remaining after the firstcombustion stage is burned in the remaining stage(s) with air ornitrogen-enriched air. All the combustion stages, except the last have aslightly rich fuel/oxidant mixture, and the last stage has astoichometric (or near stoichometric) fuel/oxidant mixture. Followingeach combustion stage, part of the energy from the combustion gases isused to perform work or to provide heat. The equivalency ratio for thefirst stage of combustion and the nitrogen-enriched air are adjusted toachieve the desired combustion temperature and reduced corrosion andpollutant levels. The equivalency ratio and nitrogen enrichmentconcentration ranges are respectively typically, phi=1.1–1.5 and 83–88%.This method of burning fuel substantially reduces the oxidant (i.e., O₂and O) and pollutant levels (i.e., NO and CO) in the effluent and, thus,allow higher operational temperatures to maintain or increase thethermal efficiency. This combustion method is applicable to many typesof combustion systems, including boilers, burners, turbines, internalcombustion engines, and many types of fuel including hydrogen andcarbon-based fuels.

Application of SCNEA to a two-stage gas turbine combustion system can besummarized. First, air is enriched in nitrogen using air separationtechnology and then compressed in a water-cooled compressor to 30atmospheres. The nitrogen enriched air enters the first stage combustionchamber where it is mixed with fuel and bums fuel rich. The combustiongases exit the combustion chamber and enters a turbine at the combustiontemperature of 1700K and the pressure of 30 atmospheres. Work isperformed in the turbine by expansion of the gases to a temperature of780 k and a pressure of 2 atmospheres. The cooled combustion gases enterthe second stage where nitrogen-enriched air or air is added to burn theremaining fuel in the second stage. The nitrogen-enriched air or air issupplied by a compressor and heated in a heat exchanger by the secondstage exhaust gases.

In a two-stage turbine cycle, the first compressor feed consists ofnitrogen-enriched air mixed with the fuel (methane for our example) at350K and a pressure of one atmosphere. The first compressor compressesthe gas mixture to the desired pressure (this compression increases thegas temperature). The mixture is then combusted at a constant pressure.Nitrogen-enriched air is used as the oxidant stream in the firstcombustion stage to allow precise control of the combustion temperature(and correspondingly the pollutant generation) while producing effluentgases that have a very low oxidant loading. The combustion products athigh temperature and an elevated pressure ace expanded to 2.0atmospheres and work is extracted (this expansion results in a loweringof the gas temperature). Since the first combustion stage is operatedfuel-rich (˜>1), there is enough fuel remaining in the effluent from thefirst combustion stage to be flammable when mixed with a stoichometricamount of air (or nitrogen-enriched air). This mixture is combusted at aconstant pressure of 2.0 atmospheres in the second combustion stage. Thetemperature of the second combustion stage is maintained below thetemperature of the first combustion stage by controlling the amount offuel remaining after the first combustion stage. The effluent from thesecond combustion stage is then expanded to 1.0 atmospheres and work itsagain extracted.

The thermodynamic cycle of compression-combustion-expansion is theBrayton cycle. For the ideal Brayton cycle, the compression andexpansion (turbine) stages are assumed to be adiabatic and isentropic,and the combustion stage is assumed to be isobaric. The efficiency ofthe Brayton cycle can be increased sometimes by increasing the maximumpressure. However, if the temperature is too low, an increase inpressure can result in a decrease in efficiency.

If the compression ratio is above 15 the temperature should be at least1400K. The low oxidant loading in the effluent when using the SCNEAmethod allows both higher temperatures and higher pressures withoutincreasing corrosion rates over those of typical combustion facilities.These allowable increases in temperature and pressure, when using theSCNEA method, lead to higher Brayton cycle efficiencies.

First Compression—The nitrogen-enriched air and methane mixture is inputto the compressor at 300K and 1.0 atmosphere. The compressor increasesthe pressure of the gas mixture to 30 atmospheres, and because thecompressor is assumes to be water-cooled, the compressed gas is assumedto exit the compressor at a temperature of 350K.

First Combustion Stage—The methane and nitrogen-enriched air mixture at30 atmospheres and 350K is input to the first combustion chamber wheremost of the methane is burned and the temperature is increased to 1700K.

The relative amount of fuel and air in the combustion mixture isdescribed by φ, the ratio of mass fuel to mass air divided by the ratioof mass fuel to mass air for a stoichometric mixture [i.e., (MassFuel/Mass Air)/(Mass Fuel/Mass Air)₂]. For φ>1 the mixture is fuel-richand for φ<1 the mixture is fuel-lean.

It is important to ensure that the gas mixture anticipated for the firstcombustion stage is flammable. Two-staged combustion with a SI enginecan be used to suppress engine knock by increasing the ignition delay.FIG. 9 shows the ignition delay as a function of the fuel-air ratio. Byoperating fuel rich in the SI engine the ignition delay is increased andthe fuel octane rating can be decreased or the compression ratioincreased before knock occurs. The fuel rich exhaust from the SI wouldbe burned in the turbine combustion chamber.

The combustion engine method described herein provides increased fuelefficiency and reduces polluting exhaust emissions by burning fuel intwo stages. The method comprises the steps of combusting the fuel in apiston engine in a first stage, the step of combusting the fuel in apiston engine in a first stage producing piston engine exhaust gases,the piston engine exhaust gases containing the fuel, combusting the fuelcontained in the piston engine exhaust gases in a second stage turbineengine, the step of combusting the fuel contained in the piston engineexhaust gases in a second stage turbine engine producing turbine engineexhaust gases, and using the turbine engine exhaust gases to superchargethe piston engine. The step of combusting the fuel in a piston engine ina first stage can be in a compression ignition engine, in a pistonengine, in a homogenous charged compression ignition engine, or in avariable compression engine, in a nitrogen enriched air combustionengine.

In one embodiment of the invention includes the step of operating thepiston engine fuel rich thereby producing a reducing atmosphere andsuppressing the formation of NOx. In another embodiment of the inventionincludes the steps of burning most of the fuel is in the piston engineand maintaining the piston engine exhaust gases sufficiently fuel richfor a second burn in the turbine engine. In another embodiment of theinvention the step of combusting the fuel in a piston engine in a firststage comprises combusting the fuel in a compression ignition enginethat has heterogeneous combustion resulting in the fuel in the pistonengine exhaust gases being at stoichiometric conditions. In anotherembodiment of the invention the step of combusting the fuel contained inthe piston engine exhaust gases in a second stage turbine engine occursat or near stoichiometric conditions at reduced combustion temperatureswhere NOx is difficult to form. In another embodiment of the inventionthe step of using the turbine engine exhaust gases to supercharge thepiston engine comprises using the turbine engine exhaust gases to drivea compressor that supercharges the piston engine. In another embodimentof the invention includes using the compressor to provides compressedair to the turbine engine for the step of combusting the fuel containedin the piston engine exhaust gases in a second stage turbine engine. Inanother embodiment of the invention the piston engine is a compressionignition engine and wherein the residence time of combusting the fuelcontained in the piston engine exhaust gases in the turbine engine isincreased to ensure that all hydrocarbons and particles are burned. Inanother embodiment of the invention the piston engine is a compressionignition engine and wherein excess air is added in the turbine engine isincreased to ensure that all hydrocarbons and particles are burned. Inanother embodiment of the invention the piston engine is a sparkignition engine that is operated fuel rich to suppress engine knock. Inanother embodiment of the invention the step of combusting the fuel in apiston engine in a first stage is combusted with an oxidizer stream. Inanother embodiment of the invention the oxidizer stream isnitrogen-enriched air. In another embodiment of the invention the stepof combusting the fuel contained in the piston engine exhaust gases in asecond stage turbine engine stage is combusted with an oxidizer stream.In other embodiments of the invention the fuel is oil, methane, naturalgas, ammonia, alcohols and/or ethers, fossil fuels (oil, natural gas,coal, etc.) inorganic fuels (ammonia, hydrazine, calcium, etc.) and/ororganic fuels (alcohols, ethers, wood, etc.). In another embodiment ofthe invention the steps of combusting takes place to perform work. Inanother embodiment of the invention the steps of combusting takes placeto provide heat. In another embodiment of the invention the heat is usedfor a furnace. In another embodiment of the invention the heat is usedfor a boiler.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and have been described in detail herein.However, it should be understood that the invention is not intended tobe limited to the particular forms disclosed. Rather, the invention isto cover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the followingappended claims.

1. A combustion engine apparatus, comprising: fuel, said fuel made up ofa first portion and a second portion, a first stage piston engine forcombusting said first portion of said fuel in a first stage, said firststage piston engine producing piston engine exhaust gases with saidpiston engine exhaust gases containing said second portion of said fuel;a second stage turbine engine for combusting said second portion of saidfuel contained in said piston engine exhaust gases in a second stage atstoichiometric conditions, said second stage turbine engine producingturbine engine exhaust gases; a supercharger for supercharging saidpiston engine using said turbine engine exhaust gases, and means fordirecting said turbine exhaust gases from said second stage turbineengine into said supercharger.
 2. The combustion engine apparatus ofclaim 1 wherein said first stage piston engine is a compression ignitionengine, a homogenous charged compression ignition engine, a variablecompression engine, a nitrogen enriched air combustion engine, arotating engine, a linear engine, and/or a reciprocating engine.
 3. Thecombustion engine apparatus of claim 1 including a compressor forproviding compressed air to said second stage turbine engine forcombusting said fuel contained in said piston engine exhaust gases. 4.The combustion engine apparatus of claim 1 wherein said fuel is oil,methane, natural gas, ammonia, alcohols and/or ethers.
 5. The combustionengine An apparatus of claim 1 wherein said fuel is any combustiblematter, comprising: a combustion engine system including fuel, said fuelmade up of a first portion and a second portion; air that is compressed;a first stage piston engine for combusting said first portion of saidfuel in a first stage, said first stage piston engine using said air andsaid fuel thereby producing piston engine exhaust gases with said pistonengine exhaust gases containing said second portion of said fuel; asecond stage turbine engine having a turbine combustion chamber; saidcombustion engine system directing said piston engine exhaust gases fromsaid first stage piston engine into said second stage turbine engine andusing said second portion of said fuel that goes into said second stageturbine engine for combustion of said piston engine exhaust gases atstoichiometric conditions in said turbine combustion chamber therebyproducing turbine engine exhaust gases, wherein said combustion enginesystem provides control that maintains said second stage turbine engineat stoichiometric conditions, said control that maintains said secondstage turbine engine at stoichiometric conditions producing turbineengine exhaust gases; said combustion engine system directing saidturbine engine exhaust gases to a supercharger to compress said air; andsaid supercharger supercharging said piston engine using said turbineengine exhaust gases, said combustion engine system maintaining saidsecond stage turbine engine at reduced combustion temperatures where NOxformation rate is low.
 6. The combustion engine apparatus of claim 5wherein said fuel is made up of any combustible matter and wherein saidany combustible matter comprises fossil fuels including oil, naturalgas, and/or coal.
 7. The combustion engine apparatus of claim 5 whereinsaid fuel is made up of any combustible matter and wherein said anycombustible matter comprises inorganic fuels including ammonia,hydrazine, and/or calcium.
 8. The combustion engine apparatus of claim 1wherein said any combustible matter comprises organic fuels includingalcohols, ethers, and/or wood.